ABSTRACT: The Peratrovich Formation and overlying Ladrones Limestone in the Craig C4 quadrangle of the Prince of Wales Island, Alaska, record the accumulation of Carboniferous carbonates behind the remnants of a Late Devonian volcanic arc in the Alexander terrane. The occurrences of declinognathodid elements in the lower Ladrones Limestone suggest the possibility of a conformable Mississippian-Pennsylvanian boundary near the base of the Ladrones Limestone. The recovery of the Early Pennsylvanian conodont Idiognathoides chaagulootus n. sp. in the lower part of the Ladrones Limestone helps to constrain current models of the paleogeographic position of the Alexander terrane during the Carboniferous because of its limited occurrence within the Uralian Seaway. The presence of Id. chaagulootus n. sp. in the Alexander terrane, the Brooks Range of Alaska, and Novaya Zemlya indicates a species level biogeographic connection between these regions that shows that the Alexander terrane remained in the Uralian Seaway until at least the Middle Pennsylvanian.